Curveball Command Could Explain Jon Lester’s Recent Woes

You know Jon Lester’s trademark curveball? It’s the pitch that looks like a fastball but evades bats by diving out of the zone. Here, let me remind you what the wipe-out offering looks like.

But there’s something noticeably off about Lester’s curve this season, which might be one reason why his K/9 in 2018 is nearly two full strikeouts lower than previous seasons. Specifically, there are two differences between Lester’s breaking pitch in 2018 as compared to what we’ve seen in the previous two seasons.

Difference #1

Lester is throwing curves to different parts of the zone this season. In the past, he would spike it down and off the plate, making batters whiff hopelessly. You can immediately see in the below heat map that he almost exclusively flipped curves down and outside the zone over the 2015-17 seasons.

Jon Lester's 2015-2017 Curveball Heatmap

But in 2018, he’s spun the pitch toward the right portion of the plate and inside the strike zone.

Jon Lester's 2018 Curveball Heatmap

I hate even typing this because I feel like I’m going to get struck by lightning while talking about Jon Lester’s curveball inefficiency. But the reality is he’s inducing only about half as many whiffs this season than previous seasons.

And since he hasn’t been able to fool batters with the curve, his overall whiff rate is almost 8 percent worse this season. That means more more opportunities for batters to knock in runs. You get the idea, so I don’t need to go on about why Lester getting fewer whiffs is bad.

Difference #2

Even though Lester is not making batters whiff anymore, he’s actually throwing curves with more horizontal movement (negative numbers in below graph = more movement).

And  Lester is also throwing curves with a touch more spin (2018: 2541 RPM; 2017: 2511 RPM).

Final thoughts

You might be concerned about Lester’s last few shaky outings, but I’m not losing sleep over it. Most important is he’s not showing signs of injury because his velocity is still strong and he’s had long stretches of success recently. For whatever reason, he’s not throwing curves to the regions in which historically have induced more whiffs, and I wonder why that’s the case.

I’m also wondering what would happen if he started throwing curves towards the same 2015-17 regions with this greater curve movement that he’s shown this year. And that’s what’s encouraging about all of this, the fact that Lester’s velocity and movement are as good as or better than ever. Now he just needs to put it together.

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